Factors influencing somatic cell count and leukocyte composition in cow milk: a field study

In recent years, there has been a proliferation of studies investigating the composition of somatic cell count (SCC) of milk, focusing on neutrophils (NEU), lymphocytes (LYM), and macrophages (MAC). These 3 components are indeed crucial for the animal's immune response to mastitis-causing pathogens. The study examined various factors influencing somatic cell count and leucocyte components in cow milk, including lactation stage, parity, and milk electrical conductivity, using data from 179 dairy cows across 6 farms throughout the entire lactation. Statistical analyses, including mixed models and logistic regression, were employed to investigate the relationships between these variables and identify risk factors for high SCC levels. Results showed that factors such as parity and lactation stage were significantly associated with somatic cell composition. In particular, the highest milk NEU values (>60% of the total leucocytic fraction) and lowest MAC values (<20%) were found at the beginning and the end of lactation, that are the critical periods for udder health. High milk electrical conductivity, low milk production, number of parity, and poor hygiene scores were identified as contributing to increased SCC. Additionally, elevated percentages of NEU and LYM in milk were associated with increased risk of high SCC values, indicating potential udder health issues.